INTRODUCTION

Rapid maxillary expansion (RME) is an orthopedic procedure widely used to correct posterior crossbite and transverse maxillary deficiency.¹ In the mixed dentition, RME produced a greater skeletal response at the level of the midpalatal suture, with a decreasing orthopedic effect toward the cranial base.^2,3 In addition, greater orthopedic effects were observed in the mixed dentition than in the permanent dentition.⁴

Because of their proximity and anatomical relationship, an increase in the transverse palatal dimensions, by default, implies an increase in the lower nasal cavity dimensions. Some benefits have been proposed to be derived from RME, including improved breathing,⁵ quality of life among mouth breathers,⁶ and decreased obstructive sleep apnea signs and symptoms.⁷

The nasal septum is an osseocartilaginous structure of the nasal cavity that supports and regulates airflow.⁸ An asymptomatic minor deviation of this septum is commonly seen as a normal developmental variation in most of the population.⁹ However, a moderate or severe nasal septum deviation (NSD) may partially obstruct the nasal airway, often resulting in predominantly oral breathing.¹⁰ Considering that the inferior insertion of the nasal septum is anatomically linked to the palate, the question arises as to whether RME could impact NSD. RME might cause an asymmetric movement of the maxillary halves.¹¹ In this sense, the lower portion of the nasal septum might follow the movement of the right or left maxillary half during symmetrical expansion.

Assessment of the impact of RME on NSD is not novel. Authors of a previous study in subjects aged 5 to 9 years suggested a positive impact of RME on the severity of NSD in the middle and lower third of the nasal cavity.¹² Bruno et al.¹³ evaluated subjects aged 8 to 12 years and suggested slight improvement in NSD after RME. In the permanent dentition, no significant changes were identified in NSD after RME.^14,15 A conventional Hyrax expander was used for RME in all these previous studies. The impact of maxillary expanders with differential opening has not been explored. Studying nasal septal deviation after RME in children is important, considering RME causes asymmetric movement of the maxillary halves that could influence the position of the nasal septum at earlier ages. A change in the position of the nasal septum could have an impact on the permeability of the upper airway.

Therefore, in this study, we aimed to evaluate nasal septum changes after RME with a differential opening expander in the early mixed dentition. Another purpose was to verify the association between quantitative and qualitative assessments of NSD. The null hypothesis was that RME does not significantly change NSD.

MATERIALS AND METHODS

This retrospective study was approved by the Ethics Research Committee of the Bauru Dental School (Protocol No. 35403520.0.0000.5417). This was a secondary data analysis of a previous randomized controlled trial (RCT) registered at Clinicaltrials.gov (NCT03705871). To detect a minimum intergroup difference of 0.05 ± 0.034 for tortuosity ratio,¹⁶ an α error of 5%, and a test power of 80%, a sample of 10 patients was required. For an estimated Spearman correlation coefficient of 0.8, considering an α error of 5% and test power of 80%, a sample of 10 patients was required.

The inclusion criteria were patients with Class I and II malocclusions, presence of unilateral or bilateral posterior crossbites in the mixed dentition, and an initial age ranging from 7 to 11 years. Patients with Class III malocclusion, craniofacial syndromes, clinical absence of maxillary deciduous canines, or history of previous orthodontic treatment were excluded. Approximately 300 patients were assessed, of whom 264 failed to meet the inclusion criteria and 12 refused to participate. The final sample included 24 participants. One of the authors enrolled the patients and assigned the participants (C.M.). All patients were treated with a differential opening expander (Great Lakes Dental Technologies, Tonawanda, NY).

The expander with differential opening had two screws with the aim of achieving a greater amount of expansion in the anterior than the posterior region (Figure 1). Both screws were concurrently activated two quarter-turns in the morning, and two quarter-turns in the evening for 6 days. Following the same protocol, only the anterior screw was activated for an extra 4 days. The amount of expansion was 4.8 mm in the posterior screw and 8 mm in the anterior screw.

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Cone-beam computed tomography (CBCT) imaging was obtained before treatment (T1) and 1 to 6 months after the active maxillary expansion phase was completed (T2) using an Accuitomo CBCT (J. Morita, Kyoto, Japan). The image acquisition protocol was 90 Kvp, 7 mA, FOV 17 × 12 cm, 17.5 seconds of exposure time, and a voxel size of 0.3 mm. The acquisition protocol was adjusted to decrease the radiation exposure as much as possible without compromising the image quality. All CBCT images were standardized with the Frankfurt plane parallel to the horizontal plane in Dolphin 3D Imaging 11.5 software (Patterson Dental Supply, Inc., Chatsworth, Calif). In the axial view, the plane passing through the center of the foramen Magnum and at the Crista Galli was positioned perpendicular to the horizontal plane.

Pre-expansion and postexpansion coronal sections passing at the center of the mesiobuccal root canal of the right maxillary permanent first molar were used. Another two frontal slices passing 5 mm forward and 5 mm backward were used. The upper limit of the nasal cavity was coincident with the cribriform plate of the ethmoid bone. The lower limit was considered as a horizontal line passing through the floor of the nasal cavity on the right side. The nasal cavity height was measured by a vertical and straight line from the upper to lower limits of the nasal cavity middle region. The nasal septum contour was measured by the length of the curve that followed the morphology of the nasal septum (Figure 2). The severity of NSD (NSD ratio) was quantified based on the ratio between the nasal septum contour and nasal cavity height, following the method of Aziz et al.¹⁴ The degree of septum deviation was indicated for a ratio value >1. The greater the ratio, the greater the septum deviation. All measurements were performed in the three sequential frontal slices. The average between measurements performed in the three slices was considered for statistical analysis.

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The CBCT sequential axial and coronal sections at T1 and T2 were also analyzed by one ear, nose, and throat (ENT) professional and four trained ENT third-year residents from the Bauru Medical School, University of São Paulo. Two ENT specialists who were professors at the Medical School trained the residents and collaborated during the study. Scores from 1 (mild septum deviation) to 3 (severe septum deviation) were assigned based on the proximity between the nasal septum and the inferior nasal turbinate, as suggested in previous studies.¹⁷ For statistical analysis, absent NSD was scored as zero. In score 1, the NSD did not reach the lower nasal turbinate. In score 2, the septum deviation reached the lower nasal turbinate. Score 3 was assigned when the septum reached the nasal cavity lateral wall, compressing the lower nasal turbinate. Figure 3 illustrates the scores assigned in the present study. When disagreement occurred in the assessment among the ENT residents, the scores assigned by most raters were used.

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RESULTS

The sample comprised 24 participants (11 male, 13 female) with a mean initial age of 7.62 ± 0.92 years. The measurements of NSD ratio showed excellent reproducibility (ICC index = 0.876), with agreement limits between 0.762 and 0.954. The ENT evaluation showed 92% agreement (weighted κ index = 0.903).

The nasal cavity height and the nasal septum contour increased after RME (P < .001). No change was observed in the NSD ratio (P = .146). The mean NSD score was similar before and after expansion (P = 1.000; Table 1).

Table 1. Interphase Changes (Wilcoxon Tests)^a

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A strong and positive correlation was found between the quantitative and qualitative analyses (r = 0.750). The NSD ratio explained 56.3% of ordinal score assigned (P < .001, Figure 4).

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DISCUSSION

The results suggested NSD changes were not observed after RME in the early mixed dentition. The lack of changes was suggested using quantitative and qualitative methods. A qualitative method completed by ENT specialists was used for the first time in this type of study. This was considered paramount, as it reflects an assessment by those who would decide whether to act if changes were meaningful.

The nasal septum is a bony and cartilaginous structure that divides the nasal cavity into two parts.¹⁸ Deviated septum is one of the most common causes of nasal obstruction.¹⁹ The diagnosis of NSD can be performed through evaluation of the nasal cavity in a radiological exam or clinical examination performed by ENT professionals.²⁰ CBCT imaging allows an accurate assessment of the morphology of the nasal septum.²¹ Asymptomatic, minor deviated septum is a normal developmental variation in most populations.⁹ In this study, we identified mild and moderate NSDs in subjects in the mixed dentition. In children, a significant NSD can affect nasal breathing, especially during physical exercise, decreasing quality of life.²² In this study, participants with a significant NSD were contacted and referred to an ENT specialist.

Nasal septum tortuosity was quantified using CBCT coronal sections of the nasal cavity. Authors of several studies have suggested that CBCT imaging is a reliable method for NSD diagnosis.^21,23 The ratio of the length of the curve value and the straight-line value defined the severity of NSD (Figure 2).¹⁴ The higher the ratio value obtained, the greater the septum deviation.

The reproducibility of quantitative and qualitative assessments for NSD was adequate with ICC >0.8 and κ > 90%. Authors of other studies who evaluated changes in the nasal septum using CBCT also showed reproducible measurements.^13,14,23 The agreement frequency for the scores of NSD was high among trained ENT residents. In addition, a strong correlation was found between the subjective analysis carried out by the ENT residents and the quantitative evaluation considering the ratio of nasal septum contour and nasal cavity height (r = 0.750). The NSD ratio explained 56.3% of the ordinal score assigned. These results suggested that quantitative and qualitative methods are reliable for accurately diagnosing NSD.

The nasal cavity height increased by 1.0 mm after RME (Table 1), in agreement with previous studies in which authors evaluated the effect of RME on the nasal cavity.^3,24 RME generally produces a skeletal increase in the dimensions of the nasal cavity in the transverse and vertical directions. The RME procedure rotates the maxillary halves laterally, causing the hard palate to move downward.²⁵ This movement is responsible for increasing the height of the nasal cavity.

The change of NSD was not significant between the pre-expansion and postexpansion phases. RME did not cause or worsen a deviation of the nasal septum, nor did it correct an existing NSD (Table 1). RME has a positive impact on all skeletal structures of the nasal cavity.² Considering that the lower limit of the nasal septum is anatomically close to the midpalate suture, the assumption was that the suture split caused by RME could facilitate some change in the nasal septum. A systematic review evaluating the effect of RME on NSD²⁶ included only one previous study in which authors evaluated changes in the nasal septum in children,¹² pointing to the limited evidence available. The results showed a potential positive effect on nasal septum asymmetry after RME during childhood, with mild straightening of the NSD. Other related studies have been published in which authors have pointed toward a tendency to mild straightening of NSD.^13,14 These findings might have been related to the increase in nasal cavity height observed after orthopedic expansion of the maxilla.

The strength of this study was the availability of an adequate sample of CBCT images before and after RME in the early mixed dentition. On the other hand, the weakness of this study was the low frequency of severe NSD in the sample.

Authors of future studies should evaluate RME effects in a sample of children with severe NSD and with functional limitations. Morphologic and instrumental functional analysis should be performed before and after maxillary expansion.

CONCLUSIONS

• After RME in the mixed dentition, an increase in nasal cavity height and nasal septum contour was observed.

• No significant change in NSD was observed after RME.

• The qualitative and qualitative analyses of NSD were strongly correlated.